We’ve been closely following recent developments at the site of BP’s disastrous 2010 oil spill in the Gulf of Mexico. There’s been a nagging stream of sightings of small oil slicks in the vicinity since August 2011, more than a year after the failed Macondo well was killed and plugged. We documented these “mystery slicks” on radar satellite images taken on August 30, 2011 and possibly again on September 11, 2011. Aerial overflights by On Wings of Care captured photos and video confirming the presence of these thin oil slicks. As we stated in our blog at that time,

Some have suggested that crude oil from the reservoir 8,000′ below the seafloor might be working its way up through faults and fractures in the bedrock, or along the Macondo wellbore. If that happens we would expect to see “seepage on steroids” as oil works its way to the seafloor along multiple pathways and floats up to the ocean surface to form persistent oil slicks.

At the time this seemed highly unlikely to me. Yet, just a few months later, Chevron lost control of a deepwater exploration well off the coast of Brazil and something remarkably similar to this scenario unfolded. Now we think it is possible that the recurring small slicks near the Macondo site might be caused by oil that leaked out of the well into surrounding bedrock during the months-long blowout, before the well was killed and cemented from top to bottom. Some oil could have escaped either via cracks and holes scoured into the severely stressed well casing, or through the pressure-relief “burst disks” that were an intentional, and controversial, part of the Macondo well design (for more details read Joel Achenbach’s excellent book, ‘A Hole at the Bottom of the Sea‘). If this scenario actually did happen, the residual oil is gradually migrating to the seafloor through existing natural fractures and faults in the bedrock, as it did in the Chevron incident off Brazil; and is seeping out of the seafloor into the water, floating up to the surface as droplets of oil and possibly oil-coated bubbles of natural gas; and forming thin slicks, behaving very much like the many natural oil seeps scattered throughout the Gulf. Eventually this residual oil will work through the system and this artificially induced “seepage” will decline, as it did in the Brazil example (Chevron has also placed structures on the seafloor to capture the oil leaks off Brazil).

But is this actually happening at the BP / Deepwater Horizon spill site?

A series of recent slick sightings, again documented by pilot Bonny Schumaker of On Wings of Care beginning on September 14, raise the possibility. There are known natural oil seeps in the general vicinity that were identified and mapped by scientists at Florida State University long before the BP spill in 2010, but the closest of these is about 2.9 miles southeast, 3.1 miles south, and 4.9 miles northeast of the plugged Macondo well. BP suggested the slicks were caused by residual oil leaking from the wreckage on the seafloor: the massive Deepwater Horizon rig, the 5,000 feet of tangled riser pipe, the failed and discarded containment devices and other pieces of equipment. In October, BP plugged the cofferdam / containment dome device that had been used in the first failed attempt to stop the Macondo spill, claiming that leftover oil leaking out of this device had been the source of the recent oil slicks. But additional slicks sighted in the area on November 2 and November 9 caused the Coast Guard to order BP to deploy more ROVs to once again investigate the site and try to identify the source of oil for the mystery slicks. BP did so in mid-December, and the Coast Guard released four low-resolution videos of that inspection operation. The videos were apparently shot on December 11-14, 2012. We haven’t watched them all but BP and the Coast Guard claim they discovered no signs of leakage from the Macondo well or the two relief wells, or from any of the wreckage. But this doesn’t address the question of possible leakage from the seafloor in the vicinity, the scenario that Chevron caused off Brazil.

The only way to answer that question is to conduct a systematic survey of the seafloor itself, not just the wellheads and wreckage. Frankly, I think in all likelihood BP has already done this, so it should be a relatively simple matter of asking them to publish a report on the results, all of the video and other data they collected, and a map showing the survey grid they executed. If a thorough seafloor survey hasn’t been done yet, then it’s time for the Coast Guard to insist, to solve this mystery in a publicly transparent way that eases everyone’s fears.

Just seeing this now, John. The spectre of this possibility has haunted us for some time. But cautious comfort may come from news that to date, the chemical analyses of surface oil near mC252 has consistently revealed alpha olefins — the sign of manmade materials such as drilling mud. We've done some preliminary calculations of the total capacity of fluids from "equipment" versus the total volume of oil that has been sighted on the surface in this vicinity. As approximate as those are, especially the latter, they still allow for the possibility that all of the surface slicks at MC252 are coming from trapped material in wreckage. If that is the case, it is finite, and we may have seen anywhere from half to two-thirds of all there will be. Much better calculations and much more information should be shared with the public, though. I honor scientific standards of not drawing premature conclusions, but that does not warrant sitting on important information and data and keeping it from the public. In my opinion. Thanks for SkyTruth's great work! –Bonny@OnWingsOfCare.org

Thanks Bonny. I still think leaking wreckage is the most likely explanation, but given the Chevron example I am now open to the possibility that some fluids — oil and gas, and the drilling mud that was pumped furiously into the well during the unsuccessful "top kill" and "junk shot" attempts — might have escaped laterally out of the wellbore. That would also be a finite amount of fluid, not the scary spectre of direct connection from the seafloor all the way down to the reservoir. But it would be something BP is responsible for. Coast Guard could demand that BP thoroughly inspect the seafloor to identify any possible leak points; measure / estimate the flow rates of those leaks; and install devices like the ones Chevron is using off Brazil to capture the leaking oil.

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